Boas

(Boidae)

Class Reptilia

Order Squamata

Suborder Serpentes

Family Boidae

Thumbnail description
Small to giant constricting snakes possessing paired lungs, cloacal spurs, and toothless premaxilla; most species are viviparous

Size
1.2–25 ft (0.37–7.7 m); 0.2–320+ lb (0.1–145+ kg)

Number of genera, species
7 genera; 41 species

Habitat
Loose sand, burrows, grasslands, savanna, forest, various freshwater habitats

Conservation status
Endangered: 1 species; Vulnerable: 4 species; Lower Risk/Near Threatened: 2 species

Distribution
South America, Central America, Mexico, southwestern Canada, western United States, and West Indies; southeastern Europe and Asia Minor; sub-Saharan western Africa east to Tanzania, north through Egypt, and Mediterranean coast from Egypt to eastern Morocco; Madagascar and Reunion Island; Arabian Peninsula; southwestern and central Asia; Indian subcontinent and Sri Lanka; Sulawesi, Moluccan Islands; New Guinea; Bismarck Archipelago; and Melanesia east to American Samoa

Evolution and systematics

Fossil snake skulls are rarely recovered because the bones of the skull are small and loosely connected and typically become separated soon after death. Vertebrae are the most common snake fossil. In general, few snake families can be identified incontrovertibly by vertebrae and ribs. Living erycine snakes, however, have several unique vertebral characters, and on this basis numerous fossil vertebrae have been identified as erycine (in the subfamily Erycinae).

The modern Boidae is believed to have descended from basal macrostomatans; it is one of several snake lineages that diverged from the primitive alethinophidians (true snakes) near the end of the Cretaceous. Macrostomatan snakes are distinguished by characters of the skull and musculature that allow them increased jaw flexibility, a greater gape, and the ability to consume larger prey.

Boid snakes share many characters with other basal macrostomatan snakes, including fully functional paired lungs, smooth scales (with some exceptions) vestiges of a pelvic girdle, and cloacal spurs. The cloacal spurs of boas are two claw-like structures that are located one on each side of the anal scale. They are usually larger in male boas than in females; the females of some species may not have apparent cloacal spurs. Characters shared with the Pythonidae, the sister taxon of the Boidae, include elliptical pupils and pitted lip scales. The pits in the lips are associated with thermoreception, the ability to detect differences in temperature.

Boas differ from pythons in numerous characters, including: Boid snakes do not have a supraorbital bone (with one exception) while all pythons have a supraorbital bone. Not all boas have labial pits; when present, the labial pits are located between the labial scales while the labial pits of pythons are centered in the labial scales. Two premaxilla are fused together to form a small bone across the front of the upper jaw; the premaxilla of boid snakes is without teeth while the premaxilla of most pythons is toothed. Most boas are viviparous, meaning they bear live young; all pythons lay eggs. Three taxa of boid snakes, Charina reinhardtii, Eryx muelleri, and Eryx jayakari, are oviparous and lay eggs.

Undoubtedly, the Boidae is more speciose than is recognized. An analysis of the geographic variation and systematic relationships of populations of Boa constrictor, the most widely distributed boid species, has yet to be accomplished. Likewise, the systematic relationships of the insular populations of all three species of Candoia remain to be investigated fully. There is little doubt that there will be further taxonomic changes within the Boidae.

As of 2002, science recognizes 41 species in seven genera and two subfamilies in the Boidae. The Boinae, the larger subfamily, includes the boas and anacondas, 27 species in five genera. The Erycinae includes the sandboa, rubber boa, rosy boa, and Calabar boa, 14 species in two genera. The division of the Boidae into these two subfamilies is based primarily on osteological characters.

Physical characteristics

The Boidae is distributed widely on five continents and countless islands and occurs in many different habitats.

Among the species, great variation in size, scalation, diet, habitat, and many other characters can be seen. There are several species of erycine snakes that are not known to exceed 3 ft (1 m) in length. The Haitian vine boa, Epicrates gracilis, is one of the most elongate and slender of all snakes. The boa constrictor is a large species, approaching 15 ft (4.6 m) in maximum length.

The green anaconda, Eunectes murinus, is the largest boid snake. Its maximum size is a topic of controversy. There are stories and reports in the literature of anacondas measuring 33–45 ft (10–14 m). Murphy and Henderson list 25 ft (7.7 m) as the longest specimen whose length actually was measured, not just estimated. This anaconda is probably the heaviest snake species in the world. While all of the giant snake species attain great weight in captivity, there are numerous records of wild specimens of green anacondas exceeding 300 lb (136 kg).

With the exception of the rosy boa, Charina trivirgata, the bodies of erycine snakes are modified for burrowing. The eyes are small and often set high on the sides of their heads, the rostrals (scales on the end of the snout) are strong and broad, and the lower jaws are underslung and close tightly. The heads are narrow and the necks thick, the bodies are round and usually smooth scaled, and the tails are short with thickened skin on the upper surfaces. Several species have blunt tails. No erycine snakes have labial pits or have been shown to have well-developed temperature-sensing abilities. The largest erycine snake is the brown sandboa, Eryx johnii; this species reaches a maximum length slightly exceeding 4 ft (1.3 m). There are several small species—the smallest is probably the Arabian sandboa, E. jayakari, with an average adult size of 0.9 ft (28 cm).

The boine snakes are mostly medium sized, athletic, terrestrial, and arboreal. The smallest species is the Abaco boa, Epicrates exsul, with a maximum length of 31.5 in (810 mm). The best-known arboreal species is the emerald tree boa, Corallus caninus. The anacondas are the largest and most aquatic of the boas; they have soft, loose skin that can withstand long periods of immersion, and their eyes and nostrils are directed upward, so that they can see and breathe with most of the head submerged. Most boine snakes have large heads that are distinctly wider than their necks, large eyes, laterally compressed bodies (to varying degrees), and long tails. Most have temperature-sensing labial pits, and several species in the genera Boa and Eunectes have temperature-sensing abilities even without labial pits.

The boas include many beautiful species. Several species have a polymorphic appearance; one such species is the Amazon tree boa, Corallus hortulanus, with patterned and unpatterned appearances that vary in color from gray to brown to yellow to orange to red. The skin of many species exhibits a beautiful iridescence. Some populations of the boa constrictor, B. constrictor, and the rainbow boa, Epicrates cenchria, have a remarkable ability to change the color of their skin; they typically appear darkest during the day and much paler at night. The Fiji Island boa, Candoia bibroni, has been seen to change from black to pale pink in a period of six hours.

Distribution

The Boidae has one of the most extensive distributions of a snake family. Several genera have disjunct distributions. In the Boinae, Boa occurs in northwestern and northeastern Mexico south through Central and South America, the Lesser Antilles, Madagascar, and Reunion. Eunectes is found in tropical South America from Colombia to Argentina. Corallus occurs in Central America from Honduras south to the Amazon drainage in eastern Bolivia and Brazil; it is found on numerous islands in the West Indies. One species of Epicrates is widespread from southern Central America and South America to Argentina; the other species are distributed throughout the West Indies. Candoia is distributed in the Indo-Pacific region from Sulawesi and the Moluccas, New Guinea, Bismarck Archipelago, Melanesia, and Polynesia east to American Samoa.

Of the Erycinae, Charina is found in western North America, including southwestern Canada, western United States, and northwestern Mexico. Charina also occurs in tropical central Africa, from Liberia east to Cameroon, Gabon, and Congo and into Zaire. In Africa, Eryx occurs in the Sahel region from Mauritania and Senegal to Kenya and Tanzania, northeastern Africa, coastal northern Africa, and the Arabian Peninsula; it also occurs in southeastern Europe, the Middle East, and Asia Minor to central Asia, India, and Sri Lanka.

Habitat

Boas can be found in nearly every habitat known to host snakes of any sort, except marine habitats. Many of the sand-boas, such as the Arabian sandboa, are well adapted to live in extremely hot and dry habitats; in contrast, Eryx tataricus is found in a very cold climate in southern Mongolia. The range of the viper boa, Candoia aspera, includes New Ireland in the Bismarck Archipelago, one of the rainiest locales on Earth. The wide-ranging boa constrictor can be found in the Sonoran Desert in northwestern Mexico, the rainforest in Brazil, and the temperate grasslands of northern Argentina.

Behavior

Boid snakes tend to be nocturnal, but they are often encountered moving or basking during the day. Faced with a perceived threat, the larger boid snakes typically defend themselves with cloacal discharge, hissing, striking, and biting. When threatened, many sandboas are reluctant to bite and instead roll into a tight ball with their heads in the center; several of the blunt-tailed species then will use their tails to mimic their heads. C. bibroni has been seen to flatten the head and the anterior half of the body, much in the manner of a cobra.

Feeding ecology and diet

Boid snakes are primarily ambush hunters that consume vertebrate prey. Ambush techniques range from that of sand-boas, which lie buried in wait for lizards or small mammals, to that of Amazon tree boas perching in trees over watercourses waiting for birds to fly by; to that of Puerto Rican boas, Epicrates inornatus, which sit high in cave entrances to intercept bats. Boid snakes can and do incorporate active foraging behavior as well.

Many small boid snakes consume lizards, both small taxa and the young of larger taxa. Anoline lizards are the favored food of many of the West Indian Epicrates. Mammals become an increasingly significant percentage of the diet as boas grow in size. Most species will consume birds whenever the opportunity presents itself. Snakes are included in the diet of anacondas, but in general snake-eating appears to be rare in the Boidae. Boas in the genera Boa and Corallus are known to caudal lure by wriggling the distal portion of their tails to attract prey. Although it does not appear to be well documented, there are a sufficient number of published reports that green anacondas kill and occasionally consume humans to assume that it does happen. It is not a common occurrence.

Reproductive biology

In most species the female is the larger sex. In some boid species, males will fight when competing to breed with a female, often incorporating wrestling and biting to achieve dominance. Male anacondas apparently do not engage in combat; groups of males are sometimes observed simultaneously courting one female.

All boine snakes and most erycine snakes are live-bearers. Litters of well-formed live young are born, typically all delivered within a short time. There is one record of a green anaconda delivering 82 young in one litter. A captive East African sandboa, Eryx colubrinus, produced more than 250 young, breeding 14 times in a 16-year period. The Arabian sandboa (E. jayakari), Sahara sandboa (E. muelleri), and the Calabar boa (C. reinhardtii) are oviparous and reproduce by laying eggs.

Conservation status

The rarest boa in the world is Corallus cropanii, known only from its type locality in southeastern Brazil. It receives no formal protection. More than 40 years have passed since the last specimen was collected, and though it has not been formally declared extinct, many authorities believe this is the case.

The Mona boa, Epicrates monensis, including both subspecies, E. m. granti and E. m. monensis, is listed as Endangered by the IUCN, owing to the fragmentation of habitat and populations, a low number of adults that is declining, habitat degradation, and introduced predators. A captive-breeding program for the species was begun in 1985, and there is now a self-sustaining captive population of several hundred individuals maintained in zoos. Reintroduction to former habitats was started in 1993, after rats and cats were eliminated from those areas. The reintroduced populations appear to be breeding.

The four species listed as Vulnerable by the IUCN are the Jamaican boa, Epicrates subflavus; Dumeril's boa, Boa dumerili; the Madagascar boa, Boa madagascariensis; and the Madagascar tree boa, Boa mandrita. At the time of this writing, all are believed to be stable.

Significance to humans

In general, few species in the Boidae are persecuted actively by humans. Most are too small to be of value in the skin trade. In the recent past, many boa species certainly were considered an important natural resource by indigenous peoples, but today it seems that most boas escape much human attention. Some of the larger boas still may be hunted for meat in remote areas, and body parts are used in folk medicine in some areas. There is commerce in the skins of anacondas and boa constrictors, but it does not approach the magnitude of the trade in python skins. With the exception of C. cropanii and Eryx somalicus, all of the boid species are kept in captivity. Boa constrictors, rosy boas, and East African sandboas are among the most commonly kept snake species; thousands are bred and born in captivity every year. As of 2002 all but three or four boid species have been reproduced in captivity.

Species accounts

List of Species

Boa constrictor

Boa constrictor

subfamily

Boinae

taxonomy

Boa constrictor Linnaeus, 1758, "Indiis" (erroneous).

other common names

English: Boa constrictor, boa, redtail boa; French: Boa constricteur; German: Konigsboa, Sbgottshlangen; Spanish: Mazacuata, travaganado, macuarel, darura; Portuguese: Jibóia.

physical characteristics

This is a medium-size to large species with a large head distinct from the neck, a laterally compressed body, and a long prehensile tail. Throughout the extensive range, there is considerable variation in pattern and color, but most boas are brown snakes with dark brown markings on the back that expand to become red, reddish brown, or dark brown blotches on the tail.

distribution

This species is found within 150 mi (240 km) of the U.S. border in northwestern and northeastern Mexico. The range includes Mexico, Central America, most of South America north of 35° south latitude. It also occurs on Dominica and Saint Lucia in the Lesser Antilles and on many small islands along the coasts of Mexico, Central America, and South America.

habitat

This adaptable species can be found in desert, grasslands, and forest.

behavior

Boas often spend much of their time in trees. Large specimens are probably more terrestrial in their habits, but even very large boas are known to climb. Boas seek shelter in the burrows of agoutis, pacas, and armadillos.

feeding ecology and diet

Boas are primarily ambush hunters. There are records of large specimens consuming ocelots and porcupines, but the typical prey includes rodents, such as rats, squirrels, agoutis, and pacas, as well as birds, monkeys, and bats. They eat large lizards, including ameivas, tegus, and iguanas. In captivity boa constrictors typically are fed mice and rats.

reproductive biology

Little is known about reproduction in the wild. In captivity boas can become sexually mature in their second year, but maturity more typically comes in the third or fourth year. Babies usually are born 120–145 days after ovulation.

conservation status

There are no baseline data regarding wild boa populations, but the species appears to be holding its own throughout its range.

significance to humans

In agricultural areas boa constrictors are important predators of rodents. Boa constrictors are commonly kept in captivity, especially in North America and Europe.

Viper boa

Candoia aspera

subfamily

Boinae

taxonomy

Candoia aspera Günther, 1877, Duke of York Island, Bismarck Archipelago.

other common names

English: New Guinea ground boa, Papuan ground boa; French: Boa nain; German: Pazifik Boa.

physical characteristics

This is a short, heavy-bodied boa with a very short tail. The head is triangular and distinct from the neck. All of the dorsal scales are keeled with a prominent, raised, longitudinal ridge that runs down the center of each scale. The maximum length of this species approaches 3 ft (1 m), but most adults are only about half that size.

distribution

The species inhabits New Guinea and the Bismarck Archipelago.

habitat

Viper boas have been encountered in coconut husk piles, on the coast under driftwood, in trees, and in leaf litter on forest floors. They often are found in swampy areas and mudflats.

behavior

This snake is nocturnal and secretive and is rarely encountered during the day except after rain. It is known to coil in a ball for defense. It also can deliver a painful bite. It is believed that this snake mimics the death adder, Acanthophis sp., in areas where the two are sympatric.

feeding ecology and diet

Viper boas commonly feed on frogs and lizards. Small mammals also are taken.

reproductive biology

Little is known about reproduction in nature. Captured gravid females have delivered litters of five to 15 babies.

conservation status

Not threatened.

significance to humans

None known.

Emerald tree boa

Corallus caninus

subfamily

Boinae

taxonomy

Corallus caninus Linnaeus, 1758, "Americae."

other common names

French: Boa canin, boa émeraude; German: Grüner Hundskopfshlinger; Spanish: Falsa mapanare verde, boa esmeralda; Portuguese: Arara bóia, cobra verde.

physical characteristics

This is a beautiful green snake highly adapted for an arboreal life. The emerald tree boa has a large head with prominently

pitted labial scales. The body is elongate and very laterally compressed, and the tail is long and very prehensile. This species has the longest teeth of any nonvenomous snake; the front teeth of a large specimen can be 1.5 in (3.7 cm) in length.

distribution

This species is known from the tropical rainforests in and surrounding the Amazon Basin of South America.

habitat

This species is associated with primary and secondary forest. It is often found in trees overhanging or near water courses.

behavior

The resting pose of this species appears to be a flat coil that is folded over a branch, with the head in the center pointing down as if to watch below.

feeding ecology and diet

Rodents, parrots, passerines, and small monkeys have all been recorded as prey.

reproductive biology

Babies are red, orange, or green. They change to the adult green color as they approach sexual maturity.

conservation status

Many Latin American countries control or forbid the export of native boid snakes; emerald tree boas thereby receive some protection from commercial collecting in most of the countries where the species occurs. The species appears to be stable and not threatened, but its future is tied to the forests it inhabits.

significance to humans

This attractive snake is popular among keepers of boas. The species is hardy in captivity and is regularly bred in captivity.

Cuban boa

Epicrates angulifer

subfamily

Boinae

taxonomy

Epicrates angulifer Bibron, 1840, Cuba.

other common names

French: Boa de Cuba; German: Kuba-Schlankboa; Spanish: Majá de Santa Maria.

physical characteristics

This is the largest species in the genus Epicrates, with a maximum size approaching 13 ft (4 m).

distribution

E. angulifer is found throughout Cuba at altitudes up to 1,000 ft (310 m); the species also occurs on nearby smaller islands.

habitat

This is an adaptable snake most often found in wooded areas, often off the ground in trees but also on rocky hillsides, in caves, and in talus.

behavior

Captive juvenile Cuban boas tend to be excitable and irritable, often biting their keepers when given the chance; adults tend to be calm and placid animals that do well in captivity. Like most boas in the genus Epicrates, the Cuban boa often excretes viscous liquid uric acid (white insoluble nitrogenous waste products) when excited or frightened.

feeding ecology and diet

Cuban boas are both ambush predators and active foragers. They are known to eat bats, rodents, chickens, native birds, and iguanas.

reproductive biology

Males fight during the breeding season. Females deliver litters of two to 10 large babies that are up to 24 in (61 cm) in length.

conservation status

Not threatened. Cuban boas are protected by Cuban law, and are believed to be common throughout Cuba. The species seems to coexist well with humans when it is not persecuted.

significance to humans

This species occasionally preys on domestic fowl.

Green anaconda

Eunectes murinus

subfamily

Boinae

taxonomy

Eunectes murinus Linnaeus, 1758, "America."

other common names

English: Water boa; huilla, huilia, camoudi; French: Anaconda commun; German: Grosse Anakonda; Portuguese: Arigbóia, boiuna, boicu, boiguacu, sucuri, sucuriju, sucurijuba, Spanish: Culebra de agua.

physical characteristics

This is a giant, heavy-bodied, dark green boa with black spots. Even an average specimen, 10–15 ft (3–4.6 m) in length, appears immense because of its girth.

distribution

This species occurs in the Amazonian and Orinoco drainages from Columbia and Venezuela to eastern Bolivia and central Brazil. It also is known from Trinidad.

habitat

The green anaconda is associated strongly with watercourses, swamps, and other freshwater habitats.

behavior

Anacondas are rarely found far from water. Feeding usually takes place in the water.

feeding ecology and diet

Anacondas typically lie in wait for prey at the water's edge. They are known to eat a wide variety of vertebrate prey, including monkeys, deer, peccaries, pacas, agoutis, birds, fish, caiman, and turtles.

reproductive biology

Breeding usually occurs during the dry season. A group of males will court a receptive female, competing peacefully to copulate.

conservation status

Not threatened. So far as is known, the green anaconda exists in reasonable numbers throughout its range.

significance to humans

Anacondas seem to be largely unmolested by humans. They are not commonly harvested for meat, and throughout most of the range there is little or no harvest of skins. Small specimens are collected and exported for the live trade, but the species is not particularly popular in captivity, largely because of its size but in part because many specimens are foul-tempered.

Calabar boa

Charina reinhardtii

subfamily

Erycinae

taxonomy

Charina reinhardtii Schlegel, 1848, originally designated as "Old Calabar, West Africa" and now annotated to "Gold Coast."

other common names

English: Burrowing python, Calabar ground python; German: Erdpython.

physical characteristics

The Calabar boa is a small species that only rarely grows longer than 30 in (80 cm). The head is small and not distinguished from the neck. The body is round, the skin is soft, the scales are smooth, and the tail is blunt. Individuals are dark brown or black with red or orange scales randomly scattered on the body. Hatchlings have white markings on their tails that disappear with age.

distribution

The species occurs in west and central Africa from Guinea and Liberia east to Cameroon, Gabon, Congo, and into Zaire.

habitat

The Calabar boa is associated with forest, soft soil, and leaf litter. It most often is seen out and moving after rains, both during the day and at night.

behavior

Calabar boas form a tight ball with the head in the middle and use the tail as a decoy. The tail of wild adults usually is scarred. So strong is the instinct for this defensive behavior that even captive-hatched and raised animals rarely will uncoil when handled. This species never bites in defense.

feeding ecology and diet

In nature the diet includes rodents and insects. In captivity the species eats rodents at all ages.

reproductive biology

The Calabar boa is oviparous; relative to body size, the eggs are immense. The eggs are delicate and thin-shelled. Clutch size ranges from one to 12 eggs; most clutches number two to four eggs.

conservation status

Not known.

significance to humans

It is reported that this species is feared by some local people, who believe that it has two heads.

Rosy boa

Charina trivirgata

subfamily

Erycinae

taxonomy

Charina trivirgata Cope, 1861, Cape San Lucas, Baja California Sur, Mexico.

other common names

French: Boa à trois bandes; German: Deistreifen-Rosenboa.

physical characteristics

The rosy boa is a small, heavy-bodied snake with a small head that is barely distinct from the neck. The eyes are small, and the pupils are vertical. The tail is relatively long and thick, coming to a blunt point. The scales are smooth and shiny. Large specimens attain considerable bulk and girth. Adult females are about 28–36 in (71–95 cm) in total length; most adult males are 18–26 in (46–67 cm). The maximum size of this form approaches 4 ft (1.3 m).

distribution

The species ranges across southern California, southwestern Arizona, and northwestern Mexico.

habitat

This is a saxicolous species, strongly associated with rocky canyons and rocky ridges and hills.

behavior

Rosy boas are usually docile snakes that are deliberate in their actions and reluctant to bite in defense.

feeding ecology and diet

Small rodents and lizards make up the bulk of the diet.

reproductive biology

A gravid female will complete a shed 16–20 days after ovulation. Usually babies are born 100–120 days after that shed. Litters typically are born from mid-August to early October. Clutch size is reported to vary from one to 13; most litters number four or five.

conservation status

Not threatened.

significance to humans

This is a very popular snake species in captivity; every year, thousands of captive-bred rosy boas are born.

East African sandboa

Eryx colubrinus

subfamily

Erycinae

taxonomy

Anguis colubrinus Linnaeus, 1758, "Egypto."

other common names

French: Boa des éscailles rugueuses; German: Aegyptische Sandboa, Kenyan Sandboa.

physical characteristics

This is a heavy-bodied sandboa with a maximum length that approaches 36 in (90 cm). The northern populations are smaller and patterned in tan and yellow, whereas the southern populations are larger and darker with an orange pattern. The undersurface is an immaculate white. The dorsal surface of the tail is armored with thick skin and hooked keeled scales.

distribution

The species is distributed in northeast Africa from central Tanzania north to Egypt and from there west into Niger.

habitat

In the northern part of the range this species is more likely found in arid sandy and rocky areas; to the south these sand-boas are found in rocky hills and in burrows in soil. They often occupy agricultural fields.

behavior

This sandboa rarely strikes forward in defense, but it defends itself with quick backward-directed slashes when its body is touched.

feeding ecology and diet

In captivity the larger animals from southern populations feed on rodents at all ages; the northern animals more often feed on geckos and skinks when they are young.

reproductive biology

Most litters contain 12–20 babies, but litters of 32 babies are reported.

conservation status

Nothing is known about this species in nature.

significance to humans

This is a very popular snake to keep in captivity; thousands of babies are born in captivity annually. The captive specimens constitute a viable self-sustaining population; very few East African sandboas are taken from the wild.

Resources

Books

de Vosjoli, Philippe, Roger Klingenberg, and Jeff Ronne. The Boa Constrictor Manual. Santee, CA: Advanced Vivarium Systems, 1998.

Greene, Harry W. Snakes: The Evolution of Mystery in Nature. Berkeley: University of California Press, 1997.

Minton, Sherman A., and Madge Rutherford Minton. Giant Reptiles. New York: Charles Scribner's Sons, 1973.

Murphy, John C., and Robert W. Henderson. Tales of Giant Snakes: A Historical Natural History of Anacondas and Pythons. Malabar, FL: Krieger Publishing Company, 1997.

O'Shea, Mark. A Guide to the Snakes of Papua New Guinea. Port Moresby, Papua New Guinea: Independent Publishing, 1996.

Pope, Clifford Millhouse. The Giant Snakes: The Natural History of the Boa Constrictor, the Anaconda, and the Largest Pythons, Including Comparative Facts About Other Snakes and Basic Information on Reptiles in General. New York: Alfred A. Knopf, 1961.

Stafford, Peter J., and Robert W. Henderson. Kaleidoscopic Tree Boas: The Genus Corallus of Tropical America. Malabar, FL: Krieger, 1996.

Stebbins, Robert C. A Field Guide to the Western Reptiles and Amphibians: Field Marks of All Species in Western North America, Including Baja California. 2nd edition. Boston: Houghton Mifflin, 1985.

Tolson, P. J., and R. W. Henderson. The Natural History of West Indian Boas. Taunton, England: R & A Publishing Limited, 1993.

Periodicals

Kluge, Arnold G. "Boine Snake Phylogeny and Research Cycles." Miscellaneous Publications, Museum of Zoology, University of Michigan, no. 178 (1991): 1–58.

——. "Calabaria and the Phylogeny of Erycine Snakes." Zoological Journal of the Linnean Society 107 (1993): 293–351.

McDowell, S. B. "A Catalogue of the Snakes of New Guinea and the Solomons, with Special Reference to Those in the Bernice P. Bishop Museum. Part III. Boinae and Acrochordoidea (Reptilia, Serpentes)." Journal of Herpetology 13, no. 1 (1979): 1–92.

David G. Barker, MS

Tracy M. Barker, MS